When Starbucks Canada offered free coffee to customers with reusable mugs Tuesday as part of Earth Day, they probably should have included some fine print.

David Schuurman of Hamilton, Ont., decided to capitalize on that oversight by going to the coffee shop with his enormous 7-Eleven Big Gulp mug, which he says holds about two coffee pots’ worth of brew.

As seen in a video Schuurman uploaded online of his prank, the barista found the whole thing as amusing as Schuurman did.

“I knew that was coming,” the man behind the counter laughs.

Starbucks has given out free coffee on Earth Day for a number of years and claims to have saved millions of pounds in paper cups, but if more people catch on to Schuurman’s loophole the cost of the giveaway might start to catch up with the company.

As for Schurrman, he may still be buzzing from the caffeine.

“It’s delicious, but I’ll be up all week,” Schuurman wrote on YouTube.